Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The amount by which the intake air is boosted or pressurized is controlled by regulating the amount of exhaust gas that is passed through the turbine housing by diverting a portion of the exhaust through a wastegate. The wastegate is opened during turbocharger operation when the boost pressure is approaching a maximum desired pressure. The wastegate diverts an amount of exhaust gas around the turbocharger turbine to reduce the rotational speed of the turbine, thereby reducing the rotational speed of the air compressor and thus the amount by which the intake air is pressurized.
In particular turbocharger constructions known in the art, the wastegate is actuated by a spring biased pneumatic actuator directly ported to the compressor outlet of the turbocharger. As a predetermined maximum boost pressure is approached, the spring bias of the pneumatic actuator is overcome and the wastegate begins opening. Alternatively, a solenoid valve is attached to the turbocharger and a sensor, either an integrated or separate, monitors the boost pressure.
In the alternative embodiments the solenoid valve varies the pressure to the wastegate actuator which, in turn, varies the wastegate position and thus the amount of exhaust diverted around the turbine, resulting in a change in turbine and compressor rotational speed and resulting boost pressure. The solenoid valve provides the means for boost control strategies, such as eliminating premature wastegate opening and delaying the initiating point for wastegate operation.
During operation of heavy-duty trucks, maximum boost pressure is desired during engine braking operation to maximize the braking power of the engine. In such circumstances, it is desirable to override or deactivate a pneumatic wastegate actuator to maintain the wastegate in the closed position. In these embodiments, a solenoid valve located between the pressure source and the pneumatic actuator is activated to divert or dump pressure from the actuator to the atmosphere, thus disabling the wastegate. The solenoid may be operated by a simple electrical connection through a microswitch activated by the brake pedal of the truck. Through an electrical control sysem, the solenoid valve may accomplish both wastegate position control and the wastegate disabling function.
A potential problem with turbocharger constructions employing a solenoid valve for either wastegate operation or override is that the valve is mounted onto the turbocharger housing in such a manner causing it to have poor vibrational characteristics, exposing it to potential physical damage. Further, external tubing interconnections are required for the valve operation. Damage potentially encountered in such constructions could be to the valve itself or could be to external hoses or fittings that are used to connect the valve to the compressor housing for venting the pressure in the wastegate actuator. Additionally, solenoid valves used in such known turbocharger constructions are typically mounted in a direction that is not aligned with any other part of the housing in a location that is close to the compressor discharger where the temperatures are the highest, subjecting the valve to potential heat damage.
It is, therefore, desirable that a turbocharger be constructed having a solenoid valve that is attached thereto in such manner to reduce or eliminate the potential for physical damage caused to it or to exposed connecting hoses by vibration, physical contact with other engine compartment components, or heat exposure.